Rainbow-electronics MAX1717 Bedienungsanleitung PDF herunterladen (Seite 21)

MAX1717

Dynamically Adjustable, Synchronous

Step-Down Controller for Notebook CPUs

______________________________________________________________________________________ 21

This can be achieved in several ways, including the fol-

lowing two (Figure 10). By using low-impedance pull-up

resistors with the CPU’s VID pins, each pin provides the

low impedance needed for the mux to correctly inter-

pret the B-mode setting. Unfortunately, the low resis-

tances cause several mA additional quiescent current

for each of the CPU’s grounded VID pins. This quies-

cent current can be avoided by taking advantage of the

fact that D0–D4 need only appear low impedance

briefly, not necessarily on a continuous DC basis. High-

impedance pull-ups can also be used if they are

bypassed with a large enough capacitance to make

them appear low impedance for the 4µs sampling inter-

val. As noted in Figure 10, 4.7nF capacitors allow the

inputs to appear low impedance even though they are

pulled up with 1MΩ resistors.

40kΩ

40kΩ 40kΩ 40kΩ 40kΩ

8kΩ

100kΩ

8kΩ 8kΩ 8kΩ 8kΩ

3V TO 5.5V

+5V

B-DATA

LATCH

GND

MAX1717

Figure 8. Internal Mux B-Mode Data Test and Latch

MAX1717

A/B

3V TO 5.5V

B-MODE VID =

01000 → 1.60V

A-MODE VID =

01101 → 1.35V

100kΩ

A/B = LOW = 1.60V

A/B = HIGH = 1.35V

Figure 7. Using the Internal Mux with Hard-Wired A-Mode and

B-Mode DAC Codes

1 2 ... 16 17 18 19 20 21 22 23 24 25 26 ... 32 33

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